1. Field of the Invention
This invention relates to a method and apparatus for reducing undesirable emissions in the exhaust of a compression ignition (diesel) engine, and more particularly, to a new and improved method and apparatus for reducing the amount of total particulates in the exhaust of the diesel engine by injecting controlled quantities of supplemental air (that may include oxygen-enriched air) directly into combustion chambers of the engine during the portion of the combustion cycle of the engine when the piston in each such combustion chamber is in its expansion and/or exhaust strokes.
2. Background of the Invention
Compression ignition (diesel) engines typically have high exhaust emissions, such as particulates (for example, carbon soot and volatile organic compounds), visible smoke, and oxides of nitrogen (NO.sub.X). The United States Environmental Protection Agency (EPA) emissions standards for future automobiles, trucks and locomotive diesel engines require simultaneous reduction of NO.sub.X and total particulate emissions to very low levels. This tends to be difficult to achieve because of the inherent tradeoffs between lowering both total particulates and NO.sub.X emissions from a diesel engine while maintaining the engine's overall fuel economy and the engine's cost efficiency. Consequently, the reduction of total particulate emissions while still meeting NO.sub.X emission standards has been an ongoing problem. In order to overcome this ongoing problem, various different methods have been tried to reduce particulate emissions. These methods include high pressure fuel injection, multiple staged injection, oxygenated diesel fuels, oxidation catalysts, and particulate traps. While it is possible in a diesel engine to reduce total particulate emissions and to improve power density performance by using oxygen-enriched intake air, such oxygen-enriched intake air tends to also increase the amount of NO.sub.X in the exhaust being emitted from the diesel engine.
In the case of both diesel and spark ignition engines, exhaust gas recirculation (EGR) systems have been used as one method of decreasing NO.sub.X emissions. When the gases from the EGR system are about 50% of the intake air, oxygen concentration is decreased from about 21% to about 14%. The decrease of NO.sub.X by the use of EGR systems tends to vary depending on the rate, temperature and water content of the EGR gases, injection timing, and air-fuel ratio of the intake to the engine. However, there are limits as to the amount of exhaust gases that can be reintroduced into the engine before power output and fuel economy are adversely affected. Such reintroduction of exhaust gases can also cause an increase in particulates in exhaust gases being emitted from the engine because the recirculated gases include soot particles.
Other attempts have been made to control the amount of NO.sub.X being emitted from the exhaust of an engine. One such method involves the retarding of the fuel injection timing, but such retarding of the injection of fuel tends to increase the amount of particulate emissions and also tends to increase fuel consumption. Another method that has been developed to control the amount of NO.sub.X generated by the engine involves controlling the amount of oxygen and nitrogen included in the intake air of the engine (see, for example, U.S. Pat. No. 5,649,517 that is assigned to the same assignee of record as the present application). On the other hand, attempts have been made to lower the level of NO.sub.X in such exhaust gases or emissions of an engine by injecting into the exhaust gases of the engine monatomicnitrogen induced by a pulse arc (see, for example, U.S. Pat. Nos. 5,526,641 and 5,640,845 that are assigned to the same assignee of record as the present application). While these systems tend to decrease the level of NO.sub.X in engine exhaust gases, they do not tend to decrease the total particulates that are present in those exhaust gases.
Accordingly, it is an object of the present invention to provide a new and improved method and apparatus for reducing total particulates in the exhaust of a diesel engine while minimizing the amount of NO.sub.X emissions in the exhaust.
It is another object of the present invention to provide a new and improved method and apparatus for reducing total particulates in the exhaust of a diesel engine by introducing controlled quantities of supplemental air (that may include oxygen-enriched air) directly into combustion chambers of the engine while the piston in each such chamber is in its expansion and/or exhaust strokes during the time that the combustion is in a diffusion and/or tail end phases of the chamber's combustion cycle.
It is still another object of the present invention to provide a new and improved method and apparatus for reducing the amount of total particulates in the exhaust of a diesel engine by introducing controlled quantities of supplemental air, that includes, at least in part, oxygen-enriched air produced by a selectively permeable membrane, directly into combustion chambers of the engine while the piston in each such chamber is in its expansion and/or exhaust strokes during the time that the combustion is in a diffusion and/or tail end phases of the chamber's combustion cycle.
It is yet another object of the present invention to provide a new and improved method and apparatus for reducing simultaneously the amount of total particulates and NO.sub.X in the exhaust of a diesel engine by utilizing both oxygen-enriched air and nitrogen-enriched air produced by a selectively permeable membrane. The oxygen-enriched air may be combined with ambient air and is injected in controlled quantities as supplemental air directly into combustion chambers of the engine while the piston in each such chamber is in its expansion and/or exhaust strokes during the time that the combustion is in a diffusion and/or tail end phases of the chamber's combustion cycle whereas the nitrogen-enriched air either is used to form monatomic nitrogen that is injected in the exhaust being emitted by the engine or is used to mix with intake air being supplied to the intake of the engine to lower the oxygen purity of the intake air.
It is still a further object of the present invention to provide a new and improved method and apparatus for reducing total particulates in the exhaust of a diesel engine by introducing controlled quantities of supplemental air (which may include oxygen-enriched air) directly into combustion chambers of the engine while the piston in each such chamber is in its expansion and/or exhaust strokes during the time that the combustion is in a diffusion and/or tail end phases of the chamber's combustion cycle and to simultaneously minimize NO.sub.X in the exhaust of the engine by either retarding the beginning of fuel injection or multi-stage injection of the diesel fuel or by recirculating a portion of the exhaust gases from the engine back into the intake of the engine (commonly known as exhaust gas recirculation--EGR).